1. The Field of the Invention
The present invention relates generally to optical transmitters. More specifically, the present invention relates to an optical transmit assembly that includes a thermally isolated laser, temperature sensor, and temperature driver for efficient heat control of the laser.
2. Background and Related Art
Computing and networking technology have transformed our world. As the amount of information communicated over networks has increased, high speed transmission has become ever more critical. Many high speed data transmission networks rely on optical transceivers and similar devices for facilitating transmission and reception of digital data embodied in the form of optical signals over optical fibers. Optical networks are thus found in a wide variety of high speed applications ranging from as modest as a small Local Area Network (LAN) to as grandiose as the backbone of the Internet.
Typically, data transmission in such networks is implemented by way of an optical transmitter (also referred to as an electro-optic transducer), such as a laser or Light Emitting Diode (LED). The laser emits light when current is passed through it, the intensity of the emitted light being a function of the current magnitude passed through the laser. Information is conveyed over an optical fiber by transmitting different optical intensities onto the fiber.
The laser has strong temperature dependencies that can seriously affect performance, depending on the application. For example, in Dense Wavelength Division Multiplexed (DWDM) laser applications, different optical channels are transmitted simultaneously, each optical channel having a tight frequency range that the corresponding optical signal should stay within. Any variance outside of the frequency range could cause inter-symbol interference (ISI), seriously increasing the error rate of the transmission. Thus, in DWDM laser applications, it is critical that the laser's transmitted frequency be tightly controlled. Nevertheless, the frequency characteristics of a laser are heavily temperature-dependent. More specifically, the frequency characteristics of the optical emissions from the PN junction of the laser are heavily dependent on temperature. Thus, in DWDM laser applications, there is tight control of the temperature of the electro-optic transducer. Although DWDM has been discussed here, there are a wide variety of applications in which it may be desirable to accurately control the temperature of the emitting PN junction of the laser.
The temperature control of the laser typically relies on a temperature feedback system. Specifically, a temperature sensor is provided in proximity to the electro-optic transducer. Depending on the sensed temperature, a temperature driver then heats or cools the temperature sensor as appropriate until the temperature sensor detects a temperature within an acceptable temperature range. The aim here is that by tightly controlling the temperature of the temperature sensor, the temperature of the proximate laser will also be tightly controlled.
However, the temperature sensor and the laser cannot occupy the same space at the same time. Therefore, the temperature sensor, though relatively proximate to the laser, is still placed some finite distance from the laser. There will thus be some finite amount of thermal resistance between the temperature sensor and the laser. If there are significant heat generating sources that are nearby to the laser and/or temperature sensor, this thermal resistance could result in significant temperature differences between the temperature sensor and the laser. Furthermore, the heat generated by the laser (from its bias and modulation currents) may also cause temperature differences between the temperature sensor and the laser. Accordingly, even very tight control of the temperature of the temperature sensor will not necessarily result in tight control of the temperature of the laser. Furthermore, significant energy may need to be expended to cool the laser should the laser receive significant heat from surrounding components.
Accordingly, what would be advantageous are mechanisms in which there is tighter and more efficient control of the temperature of the laser in an optical transmit assembly.